1. Field of the Invention
The present invention relates generally to treatment of radioactive and hazardous wastes, and more particularly to processes for immobilizing a waste containing one or more of radionuclides, hazardous elements, hazardous compounds, and other compounds present in the waste.
2. Background of the Invention
The use of radioactive and hazardous materials in the world has led to the accumulation of a significant amount of radioactive and hazardous wastes. There is an international consensus regarding the planned disposal of these wastes by burying them in the ground in deep geological repositories. At the present time, high-level radioactive wastes are being placed in long-term storage awaiting permanent disposal. Once buried, with the passage of time, groundwater and hydrothermal solutions can make contact with the radionuclides, hazardous elements, or hazardous compounds contained in the wastes. As a result, groundwater and hydrothermal solutions can facilitate the leaching of radionuclides, hazardous elements, and hazardous compounds out of the wastes into the biosphere in which plants and animals live. In addition, even without the interference from groundwater and hydrothermal solutions, radionuclides, hazardous elements, or hazardous compounds could possibly diffuse out of the wastes, resulting in contamination of the biosphere. Therefore, improper containment of the wastes can create a significant problem.
There are a number of existing processes that can potentially reduce the leaching and/or diffusion of radioactive and hazardous wastes. The existing processes, however, have various disadvantages. For example, cementation is commonly used to immobilize low-level and intermediate-level radioactive waste. This process is undesirable because a large volume of cement is required to immobilize a small quantity of wastes. Furthermore, cement is highly susceptible to both leaching and diffusion.
The most common method of handling high-level radioactive wastes is vitrification in borosilicate glass. Vitrification is currently being used in a number of countries including France, the United States of America, Korea, Italy, Germany, the United Kingdom, Japan, Belgium, China, and Russia. Conventional vitrification processes, however, are limited in the amount of waste that can be contained, and efforts to increase waste loading capacity of borosilicate glasses or melts have led to high crystallinity, increased rates of leaching, and increased corrosion of the melter, rendering the compositions unsuitable for use in conventional vitrification melters.
Thus, a need exists for improved vitrification processes and borosilicate glass compositions that achieve higher waste loading without the above-mentioned disadvantages on use of the processes and compositions with conventional vitrification melters.